Magnetic fluid grinding of ceramic balls

Magnetic fluid grinding is a process capable of material removal some 10 to 25 times quicker than is lapping, for the finish manufacturing of ball bearings. It is fast because balls, driven through a viscous fluid, are caused to skid against a drive shaft at speeds which can reach 10 m/s. Material removal is by abrasive wear caused by grits embedded in the drive shaft. In this paper it is shown that there is an optimum fluid viscosity: too small a viscosity does not cause skidding; too large a viscosity, although it causes skidding, prevents effective action of the grits in the shaft. Results are presented for the removal of material from silicon nitride, zirconia and alumina materials, over periods of up to 90 min. Abrasion is by plastic processes for the first two materials and by fracture for the last. Initially, wear coefficients range from 0.06 to 0.6. For all three, removal rates reduce with time probably due to loss of grits and to deterioriation of the fluids.